Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $226.25   9.177%   $247.013   $247.01   $247.00   $247.00  
  Purchase #2 $187.38   13.649%   $212.9555   $212.96   $212.95   $213.00  
  Purchase #3 $155.98   12.130%   $174.9004   $174.90   $174.90   $174.90  
  Purchase #4 $126.52   11.685%   $141.3039   $141.30   $141.30   $141.30  
  Purchase #5 $29.53   3.681%   $30.617   $30.62   $30.60   $30.60  
  Purchase #6 $219.72   8.268%   $237.8864   $237.89   $237.90   $237.90  
  Purchase #7 $143.33   8.769%   $155.8986   $155.90   $155.90   $155.90  
  7 purchase totals = $1,088.71       $1,200.5748   $1,200.58   $1,200.55   $1,200.60